Research on coupled biomass direct combustion power generation technology of coal-fired units

0 Introduction

Biomass energy accounts for 14% of the world's primary energy consumption and is the fourth largest energy source after coal, oil and natural gas. According to the "China Renewable Energy Industry Development Report 2019", the total amount of biomass resources that can be utilized for energy in China every year is equivalent to about 460 million tons of standard coal. Among them: the amount of agricultural waste resources is about 400 million tons, which is converted into about 200 million tons of standard coal; The amount of forestry waste resources is about 350 million tons, which is converted into about 200 million tons of standard coal. Other organic waste about 0.6 million tons of standard coal.

China's agricultural and forestry biomass power generation technology has been relatively mature, as of 2019, China's agricultural and forestry biomass power generation accumulated installed capacity of 10.8 million kW, annual power generation of 46.8 billion kWh. In September 2020, the National Development and Reform Commission, the Ministry of Finance and the Energy Bureau stipulated in the "Implementation Plan for Improving the construction and operation of biomass power generation Projects" that since January 1, 2021, new biomass power generation projects will be bidding online, and the subsidy funds will be jointly undertaken by the central and local governments, and the central part will be adjusted year by year and withdrawn in an orderly manner. This marks the future of China's biomass power generation will gradually shift from fixed electricity prices to bidding mode.

With the "30·60" carbon peak carbon neutral goal proposed, China's thermal power industry carbon emission reduction is imperative. The operation cost of flue gas decarbonization technology is high, and there is no good way to use the captured CO2, so it is difficult to promote large-scale decarbonization of coal-fired units at this stage. Biomass does not produce carbon emissions in the process of combustion and power generation utilization, so blending biomass can significantly reduce carbon emissions. The coupled biomass direct combustion power generation technology of coal-fired units has been widely studied and successfully applied in Europe and North America. Ferribridge C power plant, Drax Power Plant, Fiddler's Ferry Power Plant and Amer Power Plant in the Netherlands have all carried out successful biomass coupling transformation. Drax power plant 660 MW unit has achieved 100% pure biomass transformation. Domestic scholars have also carried out relevant research on the coupled biomass power generation technology of coal-fired units, and some power plants have carried out biomass coupling transformation, but for various reasons, most of the projects have been suspended.

The coupled biomass direct combustion power generation technology of coal-fired units has a significant effect on carbon emission reduction, and has many advantages over pure biomass burning units, which is suitable for the transformation of existing coal-fired units and for new coal-fired units. In this paper, the engineering application system design, technology and economy are studied.

1 Biomass direct combustion coupling technology route

The technical route of biomass coupled power generation mainly includes direct combustion coupling, gasification coupling and steam coupling. At present, more than 150 biomass coupling projects in Europe, the vast majority of the direct combustion coupling technology route.

Direct combustion coupling technology has low initial investment and maintenance costs and high technical maturity. According to the different coupling positions of biomass and coal, direct combustion coupling technology is mainly divided into coal mill coupling, powder pipeline coupling, coal burner coupling, independent biomass burner furnace coupling and so on.

Based on the successful practical experience in Europe, the coupling scheme of the pre-ground biomass direct injection into the powder delivery pipeline has the advantages of mature and reliable technology, simple transformation scheme, easy to quickly realize a high proportion of localization, less modification of power plant facilities, short transformation cycle, low unit cost, minimal impact on the operation and maintenance of existing power plant facilities, and good compatibility with the existing operation and maintenance system of power plant. Therefore, the coupling scheme of powder delivery pipeline can be preferred for the low proportion of biomass coupling transformation.

Different direct-combustion coupling schemes apply different biomass blending ratio. When the blending ratio is higher, the corresponding transformation cost and operation cost of coal-fired units will increase. In addition, the proportion of blended combustion is also limited by China's biomass fuel collection system, combined with the biomass fuel collection capacity of a single biomass power generation project equivalent to about 9 to 100,000 t of standard coal heat, the proportion of coupled biomass power generation of large and medium-sized coal-fired units in the short and medium term is generally within 20%, and can be increased to a higher proportion on this basis in the long term. Therefore, the choice of powder pipe coupling scheme is more appropriate in most cases. In this paper, the engineering scheme of the coupling of the powder feeding pipeline will be studied.